AF fine tune affects the green dot, but it won't make manual focusing using the green dot significantly more accurate.

10 AF fine tune units is about equivalent to the smallest movement I can make with the focus ring of a dedicated manual focus lens with a well damped focus ring. In contrast, at 50mm and f/5 the green dot is illuminated over a range about ten times larger.

I have not tried it, but what I hear is to adjust fine tune, so peak sharpness is when the indicator changes from the arrow to the dot -- of course you have to always focus from the same direction to use that technique.